1. Field of the Invention
The present invention is broadly concerned with a method and apparatus permitting simultaneous production of different output streams, and especially extrudate streams. More particularly, the invention is concerned with such methods and devices wherein an upstream barrel assembly is provided for initial processing of material, along with a downstream additive incorporation assembly serving to separate and process with individual additives a plurality of streams of the initially processed material.
2. Description of the Prior Art
Producers of pet foods very commonly wish to provide the feeds as cooked extrudates having different colors or other distinguishing characteristics such as shapes, flavors and/or aromas. In the past, it has been necessary for pet food manufacturers to provide separate extruders for the different products, which after production are mixed to give a combined feed. Alternately, it is possible to initially run a product of one color, followed by a separate run to give a differently colored product. The first alternative is objectionable because of the expense required to purchase and maintain separate extruders and related equipment (e.g., storage and metering bins, blending equipment and dust collectors); the latter approach substantially cuts overall feed production because of the need to change over the single extruder for different products.
Attempts have been made in the past to provide a single extruder or similar device capable of simultaneously producing different characterized products. For example, U.S. Pat. No. 5,486,049 describes an apparatus including means for dividing an incoming product stream so as to allow incorporation of different additives into the divided streams. However, the ""049 device is excessively complex, requiring specialized plate assemblies capable of generating a network of voids in the individual streams. Moreover, the mixing chambers include only static mixing devices, which result in very large pressure drops and the consequent need to generate high magnitude forces to propel the material through the mixing chambers.
Canadian Patent No. 1,230,005 describes a twin screw extruder device wherein the individual outputs from the twin screws of the machine are independently treated; these streams are then combined in a downstream region of the device to form a single extrudate. However, twin screw equipment is relatively expensive, and more complex than single screw devices.
The present invention overcomes the problems outlined above and provides an improved material processing apparatus designed for the simultaneous production of two differently characterized outputs or extrudates. Broadly speaking, the apparatus of the invention includes an elongated barrel presenting an outlet with an elongated, flighted axially rotatable screw within the barrel in order to move material to be processed toward and through the barrel outlet. An additive incorporation assembly is coupled with the barrel outlet and includes a flow divider having a plurality of separate outputs which is operable to separate the material passing through the barrel outlet into plural separate material streams. The overall additive incorporation assembly further includes a plurality of individual mixing chambers each including a tubular housing presenting a housing input and a housing output, and an elongated, axially rotatable mixing element within the housing. Each of the flow divider outputs is operably coupled with the input of one of the mixing chamber housings so that each of the separate material streams is directed to a respective mixing chamber. Finally, additive injectors are provided for additional of selected additives to each of the separate material streams.
In preferred forms, the plural mixing chambers (which generally number between two and four chambers, but may be in excess of this number) are in substantial axial alignment with each other and with the upstream barrel. Moreover, it is preferred that a drive coupling be provided between the barrel screw and the mixing elements such that rotation of the barrel screw effects rotation of the mixing elements. The additive injectors may be provided at or adjacent the flow divider for addition of respective additives to each of the material streams; however, these injectors may also be provided at the region of the individual mixing chambers if desired.